X-ray diffraction apparatus is used in a variety of contexts and applications.
One application is for the measurement of powder samples.
In particular, small angle X-ray scattering, SAXS, may be used to measure X-ray scattering at small angles which corresponds to features of the sample at length scales which may be for example between 1 nm and 100 nm. The small angles (2θ) used in SAXS are typically less than 5°. The smaller the angle, the larger the length scale and hence the larger the particle size, or pore size in porous materials, may be.
A beam of X-rays is typically collimated down to a very thin beam (a line) or a small spot directed to a powder sample. The X-rays scattered by the sample at small angles are detected by an X-ray detector.
For some SAXS methods it is important to work with quasi-monochromatic radiation, because it improves the normalization possibilities of the data (for higher accuracy data. Normalization may be carried out when the background from the sample holder is subtracted from the sample signal. A first measurement is carried out by measuring the sample in a sample holder and a second measurement is carried out by measuring the sample holder alone. The results are scaled and normalised and the second measurement results are subtracted from the first measurement results to get the clean contribution to the results from the sample.
It is important for accurate SAXS measurements that the collimator does not create additional disturbing scatter radiation that may influence the SAXS results.
One approach that was formerly used was to use a higly polished collimation block that blocked most of the intensity from an X-ray tube and left only a very thin beam path to hit the sample. A high quality of the collimation block was required to prevent additional scatter.
More recent set-ups for SAXS have used 1- or 2-dimensional multilayer pre-collimators to create some pre-collimation in front of a final collimator, which consists, for example, of slits or pinholes. The different types of collimators (1D or 2D) ensure that measurements down to small angles (2θ) are possible and disturbing scatter radiation that may influence the SAXS results is removed.
The pre-collimation by a 1- or 2-dimensional multilayer pre-collimator has two effects. Firstly, the pre-collimation renders the X-ray beam monochromatic. More importantly, the pre-collimation typically acts to increase the intensity of the X-ray beam by collecting and redirecting the beam from the X-ray tube before it arrives at to the collimator. The pre-collimator normally uses a parabolic or elliptically shaped mirror for one or two dimensional collimation.
Apparatus for carrying out SAXS measurement is commercially available.
Purchasers of X-ray diffraction apparatus prefer not to have to buy multiple pieces of equipment to carry out different measurements, nor to carry out extensive work to reconfigure apparatus for different measurement techniques. There would therefore be an advantage in providing an instrument that can carry out such additional types of measurement with minimal reconfiguration and in particular using the same apparatus as may be used for SAXS.